The present invention relates to an atmospheric oven utilized as a reflow oven.
A conventional reflow oven is described below with reference to FIG. 11. An oven 131 is partitioned into a preheating chamber 132, a reflow chamber 133, and a slow-cooling chamber 134. A chain conveyor 135 for transporting a substrate extends through the chambers 132, 133, and 134. In addition, each chamber has a construction for introducing nitrogen gas thereinto, and heaters 136 are provided above and below the chain conveyor 135. In this manner, the substrate 120 is uniformly heated in an inactive atmosphere. A mechanical shutter 139 or an air curtain forming means is installed on an entrance 137 of the oven 131 and an exit 138 thereof to keep the nitrogen gas atmosphere in the oven 131 at an approximately constant purity.
As shown in FIG. 12, the oven 131 has a width so that a wide substrate is allowed to pass therethrough. The heater 136 has a width corresponding to the wide substrate, and the chain conveyor 135 comprises a pair of chain guides 135a and 135b movable widthwise or horizontally according to the width of the substrate as shown by an arrow in FIG. 12.
An opening and closing mechanism of the mechanical shutter 139, mounted on the entrance 137 of the oven 131 and the exit 138 thereof to prevent the nitrogen gas from flowing outside the oven, is complicated and, as such, expensive. In addition, the opening and closing mechanism is ineffective if the interval at which the substrate is supplied to the oven is not large enough to close the mechanical shutter 139. If the air curtain forming means is installed on the entrance 137 and the exit 138 instead of the mechanical shutter 139, a large amount of nitrogen gas is consumed, and the running cost becomes high.
Further, since the oven 131 has a width corresponding to the widest substrate, the capacity of the oven 131 is great. Then, even if the size of the substrate is small, a large amount of nitrogen gas is consumed, because the capacity of the oven 131 cannot be reduced, and hence the running cost is high.